The long range goal of this project is to gain an understanding of how growing thalamocortical axons reach their targets in cortex and how the development of these thalamocortical axons affects the differentiation of cortical neurons. this project will use morphological, immunocytochemical, and laser confocal microscopic techniques to study development of geniculocortical connections in visual cortex of rats. This proposal has three major components: The first component is a morphological analysis of developing geniculocortical axons, with particular emphases on the morphology of geniculocortical axons as they grow into the cortical subplate region and as they grow from the subplate to cortical layer IV. The second component is an analysis of the morphological and neurochemical development of neurons in the subplate region and in layer IV. Both sets of experiments will be undertaken with normal and with enucleated developing rats. The third component will be an analysis of morphological development of thalamocortical projections and morphological and neurochemical development of cortical neurons maintained in organotypic tissue slice cultures. These experiments will reveal morphological and neurochemical cues important for our understanding of mechanisms by which growing thalamocortical axons can identify their target cells and how these normal developmental processes may be disturbed by early trauma-induced deafferentation.